Up to now, the access into the vehicles has been made through doors. These, although universally used, show some negative points:
they produce a lot of complexity in design and engineering; PA1 in production, they require extreme precision, to avoid defective operating and water and dust penetration; PA1 their cost is remarkable; PA1 but, above all, their functionality is deceptive; in fact, they need a log of space to be opened enough to let people in and out; PA1 in addition, each door offers one only passage and this is an important limitation, particularly where the parking areas are constricted and overcrowded--thus, it could be impossible to get out through the nearest door.